U.S. Pat. No. 3,163,261, granted to G. Sim on Dec. 29, 1964, discloses a decelerating device for a teleprinter carriage in which during most of the carriage travel the piston of the dashpot is outside of the cylinder of the dashpot. The piston is mounted to the carriage on a spring-biased friction structure in order to permit a camming surface on the dashpot cylinder to mate with a camming surface on the piston to center the axis of the piston with respect to the axis of the dashpot cylinder each time that the carriage is returned to the left margin.
Briefly, a typical teleprinter carriage is advanced from left to right across the platen and at the end of the line the carriage is returned to the left margin generally under the control of a simple spring. Under this type of control, the carriage continues to accelerate as it moves to the left and developes a rather high velocity at the terminal end of the return travel. To prevent excessive impact and damage to parts, a dashpot structure is often provided to slow the carriage as it approaches the left margin and the dashpot cylinder of the Sim patent has a central opening the size of which can be controlled by a spring-loaded cover so as to control the release of air pressure within the cylinder and thus the amount of damping generated by the piston as it moves through the cylinder.
A certain amount of clearance is necessary between the piston and the cylinder in order to accommodate manufacturing tolerances. The amount of necessary clearance coupled with the necessarily loose mounting of the piston on the carriage will permit the adverse relative orientation which can occasionally result in binding of the piston within the cylinder. This can result in loss of left-hand margin control.
Bicycle pumps have long been known in which the pistons contain flaps that are pressed against the cylinder walls by the air pressure within the compression chamber. However, such a piston is specifically intended never to leave the cylinder, much less normally enter the cylinder on each cycle of pump operation. If such a pump is disassembled, it takes a bit of work to reinsert the piston with the flap whole and properly oriented.
Therefore, it is an object of the present invention better to seal a dashpot piston.
It is another object of the present invention to seal a dashpot piston in such a manner as to permit self-centering of the piston and self-alignment and positioning of the sealing member.
It is still another object of the invention to provide a piston and cylinder structure with wide spacing between the cylinder and piston which can be accommodated by a relatively flexible seal and to provide such seal.